Defination :
It is the set of rules by which the information encoded in the nucleotide sequence of mRNA is translated into the amino acid sequence of protein.
Central Dogma:
The theory that states unidirectional flow of genetic information i.e; DNA to RNA to Protein
DNA to DNA ( Replication), DNA to RNA (Transcription), RNA to Protein (Translation)
Reverse Central Dogma
The process of formation of DNA from RNA to produce multiple RNA or synthesize protein is called reverse central dogma it seen in RNA virus
Features of Genetic Code
- It is a triplet (3) nucleotide base of mRNA complementary to DNA. i.e; TAC(DNA) to AUG (mRNA) to Methionine amino acid.
- One amino acid coded by more than one genetic code except methionine and tryptophan.
- It determine the sequence of amino acids in polypeptide chain.
- Genetic code is dictionary that help to translate language of Nucleic Acid to language of Protein.
- It is triplet of four nucleotide bases of mRNA. i.e; A, U, G, C
- There is 64 triplet nucleotide sequence combination
- Among 64 triplet combination only 61 combination codes amino acids while 3 do not code amino acid called termination codon.
- Among 61 codon 2 codon AUG (Methionine) and GUG (Valine) are Initiation codon that initiate Protein Translation.
- Remaining 59 Codon codes 19 Amino acids.
- Genetic Code is not Overlapping. eg: CATGAT = Possible(CAT, GAT) , Impossible (ATG, TGA, GAT).
- It is comma less meaning read continuously. Example AUC GGC A
UG A = AUC GGC AGA - It is non ambiguous i.e; specific to amino acids. Except GGA: Glycine, Glutamine which is ambiguous.
- It is universal. i.e; Same genetic code is used to code same amino acid in all living organisms including virus.
- Wobbling Effect: If third base of codon change there is no effect in reading of some amino acid. eg: Serine: UC
U, UCC, UCA, UCG, Arginine: CGU, CGC, CGA, CGG
Doublet Codon Quick Guide (Actually Doublet codon do not code amino acid)
AA: Asn, CC: Pro, GG: Gly, AC: Thr, CG: Arg, CU: Leu, GC: Ala, GG: Gly, UA:Tyr, UC: Ser, UG:Cys
Termination Codon: UAA, UGA, UAG
Initiating Codon: AUG, GUG
Purines: Double Ring Structured Nitrogen Base (A, G)
Pyrimidines: Single Ring Structured Nitrogen Base (T /U, C)
| 1-Letter Code | 3-Letter Code | Full Name | mRNA Codons (Complementary to DNA Sense Strand) |
| A | Ala | Alanine | GCU, GCC, GCA, GCG |
| R | Arg | ARginine | CGU, CGC, CGA, CGG, AGA, AGG |
| N | Asn | AsparagiNe | AAU, AAC |
| D | Asp | Aspartic AciD | GAU, GAC |
| C | Cys | Cysteine | UGU, UGC |
| E | Glu | GlutaMIc Acid | GAA, GAG |
| Q | Gln | GlutaMINE | CAA, CAG |
| G | Gly | Glycine | GGU, GGC, GGA, GGG |
| H | His | Histidine | CAU, CAC |
| I | Ile | Isoleucine | AUU, AUC, AUA |
| L | Leu | Leucine | UUA, UUG, CUU, CUC, CUA, CUG |
| K | Lys | LYsine | AAA, AAG |
| M | Met | Methionine | AUG |
| F | Phe | PHEnylalanine | UUU, UUC |
| P | Pro | Proline | CCU, CCC, CCA, CCG |
| S | Ser | Serine | UCU, UCC, UCA, UCG, AGU, AGC |
| T | Thr | Threonine | ACU, ACC, ACA, ACG |
| W | Trp | Tryptophan | UGG |
| Y | Tyr | TYrosine | UAU, UAC |
| V | Val | Valine | GUU, GUC, GUA, GUG |
| U | Sec | SeleNOcysteine | UGA (Sec insertion sequence) |
| O | Pyl | PyrrOlysine | UAG (Pyrrolysine insertion sequence) |
| X | Any | Unknown/Any Amino Acid | Varies |
| Z | Glx | Glutamic Acid or Glutamine | GAA, GAG, CAA, CAG |
| B | Asx | Aspartic Acid or Asparagine | GAU, GAC, AAU, AAC |
| J | Xle | Leucine or Isoleucine | UUA, UUG, CUU, CUC, CUA, CUG, AUU, AUC, AUA |